Chemical and biological reactions have been investigated in chaotic fluid flows, with particular emphasis on reactions spreading in the form of fronts, and were pointed out to have different character than in a standing or well mixed environment. The advection of small but finite size particles differs from that of point particles. The motion of raindrops in clouds has been faithfully modelled by such particles. We pointed out that populations becomes, in several cases, arranged along fractal filaments. Their dynamics exhibits therefore novel features. We carried out experiments in the field of environmental flows, applied the method of nonlinear time series analysis to environmental data, and investigated the chaotic aspects of phenomena in celestial mechanics.